Methamphetamine (MA) use is associated with accelerated progression of HIV-associated neurocognitive disorders (HAND), through poorly understood mechanisms. In addition to its well studied ability to induce oxidative stress and glial activation, MA abuse also has pronounced neurovascular effects that are reflected by an increased risk of stroke, persistent white matter hyperintensities and reductions in cerebral blood flow (CBF) in MA abusers. Consistent with this, our preliminary data show that acute MA exposure results in a significant decline in CBF in wild-type mice, as measured by laser doppler flowmetry. Thus, our central hypothesis is that: MA disrupts cerebral blood flow and elicits cerebrovascular changes that exacerbate the progression of HIV-induced neurologic disease. This hypothesis will be tested through three aims. In Aim 1, we will analyze MA's effects on cerebral blood flow. We will first test whether the effects of acute MA exposure on CBF are exacerbated in animals with underlying HIV-induced neuroinflammatory disease (using gp120 and Tat transgenic mice). We will then probe the underlying mechanism by testing whether MA-induced hypoperfusion is due to the induction of specific vasoactive eicosanoids, and in Aim 1C, we will determine whether chronic MA exposure elicits a sustained reduction in CBF in wild-type mice or in animals with underlying HIV-induced neuroinflammatory disease. Aim 2 will analyze MA's effects, alone and in combination with HIV virotoxins, on tissue microcirculation and oxygenation, and neuronal metabolism. In Aim 2A, we will test whether MA's effects on CBF are accompanied by impairment of regional microcirculation, as measured by radiotracer imaging, and by induction of hypoxic gene expression signatures (Aim 2B). In Aim 2C, we will determine whether MA exposure results in impairment of local tissue oxygenation, or changes in local neuronal oxidative metabolism, by using a highly innovative approach (in vivo two-photon nicotinamide adenine dinucleotide [NADH] imaging). Finally, in Aim 3, we will analyze MA's effects on the blood-brain barrier (BBB). HIV virotoxins and acute high-dose MA exposures have been shown to independently damage the BBB, and we will therefore test whether acute exposure to MA results in exacerbated damage to the BBB and induction of microhemorrhages in mice with underlying HIV-induced neuroinflammatory disease, as compared to wild- type mice. This will be assessed by measuring the entry of plasma proteins into the CNS and by the induction of inflammatory vascular changes. Analogous experiments will also be performed in mice with chronic exposure to MA, to determine if this results in prolonged disruption of the BBB. Results from all three aims will be correlated, to determine whether BBB disruption and microhemorrhages are associated with sustained hypoperfusion and reductions in microcirculation. Collectively, these experiments will provide new insight into the mechanisms by which MA accelerates the progression of HAND.